Depletion of a subset of 7OK stress proteins in yeast mutants shows that they are involved in the post-translational import of precursor polypeptides into both mitochondria and the lumen of the endoplasmic reticulum. The identification of such a basic function may explain the remarkable evolutionary conservation of the gene family encoding these proteins.

A subfamily of stress proteins facilitates translocation of secretory and mitochondrial precursor polypeptides

A yeast cytosol is shown to contain two distinct activities that stimulate protein translocation across microsomal membranes. One activity was purified. It consists of two constitutively expressed 70K heat shock related proteins that increase the rate of translocation. Possible mechanisms of action of these proteins are discussed.

70K heat shock related proteins stimulate protein translocation into microsomes

https://epub.ub.uni-muenchen.de/7513/1/Neupert_Walter_7513.pdf

Mitochondrial protein import.

A Rab Protein Is Required for the Assembly of SNARE Complexes in the Docking of Transport Vesicles

Many newly synthesized proteins must be translocated across a membrane to reach their final destinations. Translocation requires a signal on the protein itself, a loose conformation of the protein, energy, and receptor-like components in the cytosol and on the target membrane.

https://science.sciencemag.org/content/sci/241/4871/1307.full.pdf

Protein translocation across membranes

We describe an in vitro system with all components derived from the yeast Saccharomyces cerevisiae that can translocate a yeast secretory protein across microsomal membranes. In vitro transcribed prepro-alpha-factor mRNA served to program a membrane-depleted yeast translation system. Translocation and core glycosylation of prepro-alpha-factor were observed when yeast microsomal membranes were added during or after translation. A membrane potential is not required for translocation. However, ATP is required for translocation and nonhydrolyzable analogues of ATP cannot serve as a substitute. These findings suggest that ATP hydrolysis may supply the energy required for translocation of proteins across the endoplasmic reticulum.

/pdf/secretory-protein-translocation-in-a-yeast-cell-free-system-xcmsvhhvpp.pdf

M G Waters

Papers

Secretory protein translocation in a yeast cell-free system can occur posttranslationally and requires ATP hydrolysis.